The expected functionality is that if we're deleting a value no new value should be needed. However the once a value is deleted the form requires one and will not update without.
This has been resolved in Service Pack 17. Please download and install the latest Service Pack or Hot Fix which contains all fixes from previous patches.
Steps to Duplicate
1. Add a new global change. 2. Choose the type:Manage purpose or designation attributes 3. Complete the required fields. 4. Select 'Start date' from the available fields. 5. Set the action type for 'Start date' to 'Delete value if it exists'. 6. 'New value' field is required.